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In this work, silver nanoparticles (AgNPs) were synthesized from cashew nutshell liquid (CNSL) by varying the concentration of silver ions and the pH of the CNSL extract. The synthesized AgNPs were further characterized to study their surface, structural, and morphological properties and tested for the removal of methylene blue (MB) dye. The results of this study showed that depending on the conditions, particles of various sizes, ranging from 1 to 60 nm, and different degrees of stabilization and agglomeration were produced. The concentration of silver ions equal to 3 mM and the pH of the extract of ~4.5 (AgNP3) resulted in the most efficient synthesis, where particles appeared to be highly stabilized and homogeneously distributed on the surface, exhibiting a small average particle size and a narrow particle size distribution (6.7 ± 6.5 nm). Such particles further showed the highest percent removal of MB, where up to 80% removal was recorded within the first 20 min. Higher concentrations of silver ions and higher pH of the extract resulted in substantial particle agglomeration and particles being over-capped by the CNSL biomolecules, respectively, which further negatively affected the ability of particles to remove MB. Finally, the fact that visible light showed no significant effect on the removal of MB, with the average removal rates found to be about the same as in the dark, suggests the strong catalytic nature of AgNPs, which facilitates the electron transfer reactions leading to MB reduction.

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In this work, Ni-doped ordered nanoporous carbon was prepared by a simple and green one-pot solvent evaporation induced self-assembly process, where chestnut wood tannins were used as a precursor, Pluronic® F-127 as a soft template, and Ni2+ as a crosslinking agent and catalytic component. The prepared carbon exhibited a 2D hexagonally ordered nanorod array mesoporous structure with an average pore diameter of ~5 nm. Nickel was found to be present on the surface of nanoporous carbon in the form of nickel oxide, nickel hydroxide, and metallic nickel. Nickel nanoparticles, with an average size of 13.1 nm, were well dispersed on the carbon surface. The synthesized carbon was then tested for the removal of methylene blue under different conditions. It was found that the amount of methylene blue removed increased with increasing pH and concentration of carbon but decreased with increasing concentration of methylene blue. Furthermore, photocatalytic tests carried out under visible light illumination showed that purple light had the greatest effect on the methylene blue adsorption/degradation, with the maximum percent degradation achieved at ~4 h illumination time, and that the percent degradation at lower concentrations of methylene blue was much higher than that at higher concentrations. The adsorption/degradation process exhibited pseudo second-order kinetics and strong initial adsorption, and the prepared carbon showed high magnetic properties and good recyclability.

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Activated carbons prepared from cashew nut shells by chemical activation with phosphoric acid were tested for the removal of acetaminophen. It was found that an increase in carbonization temperature resulted in increased pore volume and decreased amount of surface functional groups. Potentiometric titration analysis indicated that the majority of surface groups on carbons are acidic. Detailed surface characterization by FT-IR, XPS, and thermal analyses indicated the involvement of surface functional groups in the removal of acetaminophen either via hydrogen bonding or by acid hydrolysis. The carbon obtained at 600 °C, which contains high amount of carboxylic groups and high pore volume, exhibited the highest adsorption capacity. For this carbon, the removal of acetaminophen took place mostly via acid hydrolysis with the formation of p-aminophenol and acetic acid adsorbed on the surface. Carbon obtained at 400 °C was found to have the highest density of acidic functional groups, which resulted in dimerization reactions and pore blockage. No direct correlation was observed between the adsorption capacities of carbons and their textural or surface characteristics. This suggests the complexity of acetaminophen removal by the cashew nut shell-derived activated carbons, governed by their surface chemistry and supported by high surface area accessible via micro/mesopores.

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Two graphite oxides (GOs), obtained by oxidation of graphites of different origins, were used as composite components with copper-based metal-organic frameworks, MOFs. Such composites were tested for ammonia adsorption at room temperature, in dry and moist conditions. The materials were characterized by X-ray diffraction, FT-IR spectroscopy, adsorption of nitrogen, and thermal analysis. Generally, the ammonia adsorption capacities of the composites were found to be lower than those calculated for the physical mixture of their components. An involvement of NH3 adsorption sites of MOF in a composite formation was found to be a major factor, lowering the adsorption capacity of a composite in dry conditions. The composites with the smaller amount of GO were found to be better adsorbents of ammonia in the absence of moisture than those, with the higher amount of GO. The adsorption of ammonia in moist conditions resulted in a collapse of MOF structure, accompanied by the release of active groups. These groups contributed to the enhanced adsorption of ammonia via acid-base reactions. Thus, in the presence of moisture, the composites with the higher amounts of GO, and the ones, containing more carboxylic groups than epoxy groups in GO, were found to be the best performing samples.

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Adsorption of NO(2) and retention of NO (the product of NO(2) reduction by carbon) on iron-containing materials prepared from polystyrenesulfonic acid-co-maleic acid iron salt were studied. The surface of the materials was characterized using nitrogen adsorption, XRD, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), and FTIR spectroscopy, and thermogravimetric analysis (TGA). The results showed the positive effects of the pore volume and well-dispersed iron species (Fe(2)O(3), FeSO(4), and FeS) on the performance of carbons as NO(2) adsorbents at room temperature. The retention of NO(2) on the carbon surface takes place either through its reduction to NO by carbon and/or by Fe(2)O(3), FeSO(4), and FeS, or through its reaction with Fe(2)O(3) and/or Fe(OH)(3), leading to the formation of Fe(NO(3))(3). The retention of NO is enhanced on carbons containing iron in the form of α-FeOOH, α-Fe(2)O(3), or γ-FeOOH. The best performance was found on the carbon with α-Fe(2)O(3). Dispersion and the particle size of iron compounds on the carbon surface affect both the adsorption/reduction process of NO(2) and the retention process of NO.

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Wood-based activated carbon was modified by deposition of silver using Tollens method. Adsorbents with various contents of silver were used to study NO(2) and NO (the product of NO(2) reduction by carbon) retention. The surface of the initial and exhausted materials was characterized using adsorption of nitrogen, XRD, SEM/EDX, FTIR and TA. The results indicated that with an increasing content of silver on the surface the capacities to retain NO(2) and NO increase until the plateau is reached. The performance depends on the dispersion of nanoparticles and their chemistry. Highly dispersed small silver metal particles promote formation of chelates with NO(2) and/or with NO. An excess of Tollens reagent results in formation of larger silver crystals and silver oxide nanoparticles. If sufficiently dispersed, they also enhance the retention of NO(2) via formation of nitrates deposited in the pore system. The surface of the carbon matrix is also active in NO(2) retention, providing the small pores and edges of graphene layers, where the reductions of NO(2)/oxidation of carbon take place.

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Interactions of NO(2) and NO (the product of NO(2) reduction by carbon) with biomass-based carbonaceous materials with silver nanoparticles deposited on the surface were studied. The surface of the materials was characterized using adsorption of nitrogen, X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and thermogravimetric analysis (TGA). The results showed that the amount of NO(2) adsorbed, its conversion to NO, and the amount of NO released from the carbon surface depend on the carbon's content of silver. More silver results in a better performance of the adsorbent. The products of NO(2) interactions with silver include surface chelates such as Ag(2)-O-NO or Ag-O(2)-NO. Another element, active in the surface reactions with NO(2), is phosphorus. Both silver and phosphorus species are oxidized by NO(2). The product of NO(2) reduction, NO, is either retained on the carbon surface by its interactions with metallic silver or is further reduced to N(2)O or N(2). Besides silver, carbon support is also active in the reduction of NO(2) to NO. Carbon monoxide formed in such a processes can reduce silver oxide nanoparticles, and thus, it provides more metallic silver for interactions with NO.

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The removal of NO(2) on urea-modified and heat-treated wood-based activated carbons was studied. From the obtained results it was found that these modifications, especially when done at 950 degrees C, have a positive effect on NO(2) adsorption and on the retention of NO (the product of NO(2) reduction by carbon). The presence of moisture in the system enhances the removal of NO(2) but negatively affects the retention of NO. It is possible that the formation of active centers on the carbon surface and some increase in the volume of supermicropores during the high temperature treatment play a significant role in these removal processes. The surface of the carbons was analyzed in terms of the pK(a) distributions. The qualitative and quantitative analyses of the NO(2) adsorption products were carried out by means of FTIR and TA techniques, respectively. The main products found on the carbon surface were the NO(3) and NO(2) species.

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Activated carbons of different origins were studied as methyl mercaptan adsorbents in wet, dry, and oxidizing conditions. The materials were characterized using adsorption of nitrogen, Boehm titration, and thermal analysis. Investigation was focused on the feasibility of the removal of methyl mercaptan on activated carbons and on the role of surface chemistry and porosity in the adsorption/oxidation processes. The results showed relatively high capacities of carbons for removal of CH3SH. The amount adsorbed depends on the surface features. Methyl mercaptan, in general, is oxidized to disulfides, which, depending on the chemistry of the carbon surface, can be converted to sulfonic acid due to the presence of water and active radicals.

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